This invention applies to the field of illumination projectors, including fiber optic projectors, slide projectors, video projectors, movie projectors and overhead slide projectors. These projectors normally use low-voltage (12 to 15 volt) quartz-halogen lamps operating at color temperatures above 3100.degree. K. Lamps operated in projectors usually have a relatively short operating life.
Currently known prior-art projectors are difficult to service. Since lamp failures often occur while the lamp is hot, and the user must allow the projector to cool before attempting lamp replacement. Then, after cool-down, access to the lamp is usually through some kind of door. Since lamp pins fit tightly into the lamp socket receptacles, the lamps require substantial force and dexterity to remove, particularly when manipulated through a door opening. Then the new lamp must be inserted through the same doorway, but with the warning restriction that touching the quartz bulb with the fingers will cause premature lamp failure.
Once installed, quartz-halogen lamps are intensely hot, requiring a cooling fan to keep lamp seal temperatures within operating limits. This lamp cooling requirement is addressed by the applicant's U.S. Pat. Nos. 5,099,399 and 5,263,874. The Lamp filament is supported within the lamp envelope or "bulb".
Most projector manufacturers, as well as users, tend to rely on the lamp manufacturers' data on expected lamp life. However, lamp life tests are conducted on a stationary test bench at standard room temperature. The test lamps are operated at rated D.C. voltage to determine the published average number of burning hours before failure.
Test bench lamp failures occur as a tiny imperfection in the tungsten filament causes higher local resistance and higher heat than adjacent filament areas. Therefore, the filament spalls off tungsten atoms from the hottest spot, developing "notching" that eventually results in what is known as a "burned-out" lamp filament. However, projection lamps are not operated on a vibration-free test bench at room temperature and rated D.C. voltage. Instead, they are operated at low-voltage alternating current, much higher ambient temperature, in a housing with a vibrating fan that sweeps the potential resonant frequencies of the housing, the chassis, the lamp bracket and the lamp filament each time the fan starts or stops.
Extensive testing of lamps in fan-cooled projectors by the applicant has shown that the lamps normally do not operate long enough for typicalnotching failures to occur. Lamps that are rated for 1,000 hours fail in as little as 250 hours, and they fail in a different mode. The filament failure mode for fan-cooled projector lamps is a premature failure in which the filament support wires break off at their juncture with the glass bulb. The premature lamp failure is caused by the fan-induced vibration of the hot lamp filament supports.
A principal disadvantage of prior art projectors is that they do not recognize vibration as a primary cause of lamp failure, and hence to not provide isolation between the vibrating fan and the vibration-sensitive lamp. It is therefore a rare occasion when projector lamp life approaches the published lamp life. Another disadvantage of prior-art projectors is that the frequent lamp replacement is made quite difficult by the limited access through an access door.
Extensive tests by the applicant has shown that vibration isolation of the lamp from the fan can substantially eliminate filament vibration and restore projection lamp life to approximately the bench-test life published by the lamp manufacturer.
The primary purpose of the present invention is to provide a light projector in which the lamp is supported on a chassis that is easily removed from the projector housing for service and lamp replacement. It is a further purpose of the invention to a projector in which the lamp is isolated from fan vibration; thereby greatly increasing actual lamp life in service. It is yet another purpose of the invention to a projector in which all the electrical components of the projector are mounted on an easily-replaced chassis, facilitating on-site service, wherein all service, including lamp replacement may be done on a bench.